This invention relates to an apparatus for testing the airtightness of watches, such as wristwatches, in order to judge their acceptability in waterproofness, more specifically to an apparatus examining the waterproofness of a watch by putting the watch in an airtight container, pressurizing or decompressing the interior of the container, and detecting a change of distortion of the watch caused by such pressurization or decompression to measure the degree of the airtightness of the watch.
Conventionally, there are two methods for testing the waterproofness of watches, especially wristwatches. One of these methods is an ocular check method to ascertain if any bubbles come out of a watch immersed in water, while the other is to measure a distortion of the watch caused by a change of air pressure.
With the former method, a watch to be examined will be penetrated by water if it is suffereing from any substantial leak. Such trouble would be fatal to some watches which incorporate electronic circuits. Moreover, this method lacks in accuracy because it depends on the ocular observation.
Thereupon, the latter method has recently come into general use. This conventional method, however, has such drawbacks as mentioned below.
A prior art testing apparatus utilizing the change of distortion of a watch, for example, is so constructed that a moving iron core placed on the watch is moved by a change of distortion of the watch accompanying a change of pressure inside an airtight container, thereby changing the reactance of a coil, and that the degree of the distortion of the watch or the acceptability of the airtightness of the watch may be judged from the variation of reactance.
In such prior art apparatus, however, the reactance change has no linearity, that is, the variation of reactance is not in direct proportion to the distortion of the watch, so that it is difficult to make a quantitative measurement of the leak from the watch. Since the moving iron core is relatively heavy, it will cause the watch a substantial initial distortion when it is placed on the watch, thereby making it hard to grasp an accurate change of distortion of the watch. In order to detect the reactance, moreover, there are required a stabilized AC power source to excite the coil and a rectifier circuit for converting detected AC voltage into DC voltage. As a result, a detector circuit and a display circuit to notify an operator of detected information will be complicated in construction, and the apparatus as a whole will be increased in cost.
In another example of a prior art testing apparatus of this type, a coil connected to an external reactance measuring device is disposed untouched opposite a watch to be examined, a magnetic film is pasted on the facing surface of the watch, and a distortion of the watch caused by a change of pressure is detected as a reactance change. Despite the advantage of the untouched detection, in this case, the operation efficiency for testing is very low because of the trouble of pasting a magnetic film on the surface of each watch to be examined, as well as of tearing the film from the watch after each test.